The first project was created with Qt 4.7.4 (mingw 4.4) and an old version of Qt Creator.

My first step was to upgrade to Qt Creator 4.4.1, keeping Qt 4.7.4 (mingw 4.4).
The project compiles and runs.
However I have this warning:
"C:\Qt\mingw\bin\g++.exe" is used by qmake, but "C:\Qt\mingw\bin\mingw32-c++.exe" is configured in the kit.
Please update your kit or choose a mkspec for qmake that matches your target environment better."
The kit is defined like this:

The second step is to upgrade to Qt 5.8 (mingw 5.3).
Compilation succeeds. But execution fails directly at the beginning.
The kit is defined like this:

Qt and Mingw were installed with Qt Maintenance Tool.

Perhaps my compiler is not correct?
Do you have any idea?
Ask me if you need more infos about merkaartor libs or my .pro.
Thanks by advance for your advice.

I'm afraid this has nothing to do with your compiler issues. You probably know a lot more about this than I do, but QtWebKit got dropped by Qt for QtWebEngine at Qt 5.7. This keeps coming up and I'd like to understand: are you able to continue to use QtWebKit because you compile source code from that link, and that still works? Thanks.

The debugger is "C:\Program Files (x86)\Windows Kits\8.0\Debuggers\x86\cdb.exe".
I've tried with the debugger "GNU gdb 7.10.1 for MinGW 5.3 32bit", it crashes before the breakpoint in the main.

I've created an empty Qt widget application with Log4Qt alone. Compilation and execution ok.
I've added Merkaartor to this project and it crashes.
I also use libraries: libgdal and libproj for example.